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Rewinding a MOT for 300-450VAC

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GrimX9

Wed Sept 22 2010, 02:51AM

Registered Member #3225 Joined: Wed Sept 22 2010, 02:14AM
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Posts: 24

So, I recently removed all of the windings on the secondary of a 1200 Watt MOT, and I am planning on winding it for 300-450VAC output. However, as I continue to wind it (using 18 gauge NON LAMINATED WIRE) The winds to voltage ratio continues to drop, first it was around 1.2VAC per winding, now its about 0.8VAC per winding. As I need 300VAC at least (Ideal calculations put output power at around 4amps, not including resistance of the wire, efficiency of the transformer, etc), Is it possible to safely use a smaller gauge wire? According to several wire gauge guides, I could use wire as small as 22 gauge and safely handle several amps. My real concern is, will a rewound MOT be able to output around 300-450VAC? Most rewound MOT's I have seen are either arc welders, or low voltage power supplies. The output will be rectified into DC to charge capacitor banks, as I am tired of using low power DCDC converters that take a minute to charge a bank.

TLDR: Can a MOT output a voltage between 300-450 is properly rewound? If this is not possible, can you suggest a high power DCDC converter? I am familiar with handling high voltages and electronics, so none of this is really a problem for me.

EDIT: Great to finally join 4HV! Ive used this site many times for reading articles, but never bothered to join the forum.

Patrick

Wed Sept 22 2010, 03:13AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

well, i think the answer to your question is yes. i would use 20 Ga. you can get 4.8 amps on the standard current density, also if you can snag some magnet wire youll be able to get more turns then plastic coated wire.

EDIT: what will be your duty cycle? you can use thinner wire, for shorter time and get the same temp rise.

GrimX9

Wed Sept 22 2010, 03:25AM

Registered Member #3225 Joined: Wed Sept 22 2010, 02:14AM
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Posts: 24

Yes, my primary has been completely unmodified. The transformer was originally a 1200W 120VAC primary 60Hz MOT transformer, pretty run-of-the-mill. Should I use my current wire (plastic like insulation, not PVC, not laminated 18 gauge) or change to magnet wire of some different size?

Patrick

Wed Sept 22 2010, 03:51AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i prefer magnet wire whenver possible.what was the secondary output?

radiotech

Wed Sept 22 2010, 04:33AM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
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Posts: 1546

I do not know what you mean here :

The winds to voltage ratio continues to drop, first it was around 1.2VAC per winding, now its about 0.8VAC per winding

Do this : wind 10 test turns around the outside of the old primary(first layer). make voltage test.

Then make a cardboard filler to simulate the thickness of the new winding Then make another test winding of 10 turns (now longer)
and run the voltage test. (last layer)

Whan you make these test with a DVM connect a 100 ohm resistor across the prods.

Do these two voltage tests agree?

Patrick

Wed Sept 22 2010, 04:40AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

thats a good idea radiotech, i would have caught that but i was asleep at the switch.

volts per turn should be constant as the primary/core is what decides this factor.

GrimX9

Wed Sept 22 2010, 03:52PM

Registered Member #3225 Joined: Wed Sept 22 2010, 02:14AM
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Posts: 24

I miscounted the windings

, so actually im still getting 1.2v per winding. I with about 20 windings, I am running out of space, so no way I'd be able to get 280 more. I will be using 24 or 22 gauge enameled wire instead.

Patrick

Wed Sept 22 2010, 04:36PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i think you can get away with 22 Ga@ @ 4.8A, but 24 might be your limit, any less you might burn your secondary.

GrimX9

Wed Sept 22 2010, 04:38PM

Registered Member #3225 Joined: Wed Sept 22 2010, 02:14AM
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Posts: 24

Thanks, 22 gauge enameled is a lot smaller than the 18 gauge with Teflon insulation that was on there.

radiotech

Wed Sept 22 2010, 05:45PM

Registered Member #2463 Joined: Wed Nov 11 2009, 03:49AM
Location:
Posts: 1546

The largest size wire that you can fit in will give the best regulation.
If you remove the magnetic shunts,

The idea is to drive the percent impedance down. This is the percent of primary voltage that you can apply to reach rated primary current. (1200watts/primary voltage) It is tested with a variac and a clip-on ammeter.

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